The skeletal system includes many long bones that extend from the human torso. These long bones include the femur, fibula, tibia, humerus, radius and ulna. These long bones are particularly exposed to trauma from accidents, and as such -often are fractured during such trauma and may be subject to complex devastating fractures.
Automobile accidents, for instance, are a common cause of trauma to long bones. In particular, the femur and tibia frequently fracture when the area around the knee is subjected to a frontal automobile accident.
Often the distal end or proximal portions of the long bone, for example the femur and the tibia, are fractured into several segments and must be realigned. Mechanical devices, commonly in the forms of pins, plates, screws, nails, wires and external devices are commonly used to attach fractured long bones. The pins, plates, wires, nails and screws are typically made of a durable material compatible to the human body, for example titanium, stainless steel or cobalt chromium alloys.
Fractures of the long bone are typically secured into position by at least one of three possible techniques.
The first method is the use of intramedullary nails that are positioned in the intramedullary canal of those portions of the fractured bone.
A second method of repairing fractured bones is the use of internal bone plates that are positioned under the soft tissue and on the exterior of the bone and bridge the fractured portion of the bone.
Another method of securing fractured bones in position is the use of external fixators. These external fixators have at least two general categories. In one category the fixator is generally linear with a first portion of the fixator to connect to a first fracture segment of the bone and a second fracture segment of the fixator to connect to the second fracture segment of the bone. A first series of bone screws or pins are first connected to the fixator and then into the first portion of the bone. Then a second series of screws or pins are connected to the fixator and then to the second fracture segment of the bone, thereby securing the first portion fracture segment of the bone to the second portion of the bone.
A second method of external fixation is through the use of a ring type fixator that uses a series of spaced-apart rings to secure the bone. For example, an upper ring and a lower ring are spaced apart by rods. A plurality of wires is placed through the long bone and is connected on each end of the long bone by the ring. The wires are then tensioned much as spokes in a bicycle are tightened, thereby providing for a rigid structure to support the first fracture segment portion of the bone. Similarly, a plurality of wires are positioned through the second fracture segment of the bone and are secured to and tensioned by the lower ring to provide a rigid fixation of the second fracture segment of the bone bridging the fracture site.
There are a variety of devices used to treat femoral fractures. Fractures of the neck, head or intertrochanter of the femur have been successfully treated with a variety of compression screw assemblies, which include generally a compression plate having a barrel member, a lag screw and a compressing screw. The compression plate is secured to the exterior of the femur and the barrel member is inserted into a predrilled hole in the direction of the femoral head.
The lag screw, which has a threaded end and a smooth portion, is inserted through the barrel member so that it extends across the break and into the femoral head. The threaded portion engages the femoral head. The compressing screw connects the lag screw to the plate. By adjusting the tension of the compressing screw the compression (reduction) of the fracture can be adjusted. The smooth portion of the lag screw must be free to slide through the barrel member to permit the adjustment of the compression screw.
Subtrochanteric and femoral shaft fractures have been treated with the help of intramedullary rods, which are inserted into the marrow canal of the femur to immobilize the femur parts involved in fractures. One or more single angled cross-nail or locking screw may be inserted through the femur and the proximal end of the intramedullary rod. In some varieties, one or two screws may also be inserted through the femoral shaft and through the distal end of the intramedullary rod. The standard intramedullary rods have been successfully employed in treating fractures in lower portions of the femoral shaft.
Similarly, the tibia shaft fractures are frequently treated with the help of intramedullary rods. The intramedullary rods are inserted into the marrow canal of the tibia to immobilize the tibia parts involved in the fractures. Transverse screws may be inserted in apertures formed in the intramedullary rod. The transverse screws are secured to the cortical bone of the tibia.
In both femoral shaft fractures and tibial shaft fractures when intramedullary rods are used the proper transverse screw must be selected for use in the transverse openings of the intramedullary rod after the bone shaft has been drilled to prepare the bone for receiving the transverse screw. It should be appreciated that with other intramedullary rods, such as those for the humerus or any other long bone in the body, the same concern about selecting the proper transverse screw for the intramedullary rod assembly is needed.
The proper length of the transverse screw for use with the intramedullary rod preferably has sufficient length to receive both cortices of the bone shaft. Also, it should be appreciated that the screw is preferably no longer than necessary to engage both cortical walls so that the minimal soft tissue damage occurs.
Several prior art attempts have been utilized to measure the distance between the medial and lateral cortical surfaces of a long bone, for example, a tibia. For example, Smith & Nephew, Memphis, Tenn., has a separate drill guide and measuring instrument. Screw length measurements are accomplished by laying a callipered instrument over the leg and taking an x-ray image of the anterior-posterior view. The measurement is read from the image. The requirement of an x-ray image adds significant time to the procedure and exposes the patient to more radiation than is otherwise necessary.
Stryker Corporation, Kalamazoo, Mich., provides a screw length-measuring device in which the length of the distal screw is measured by drilling the bone, then sliding a gage, which is semi-circle in cross-section on the drill bit. The surgeon is required to hold the measuring device against the drill bit while he takes the reading.
Synthes, Switzerland, provides a procedure for measuring the length of the transverse screw which includes the steps of drilling the bone, removing the drill and drill bit, and inserting a depth gage into the drilled hole for measurement of the required screw length. This procedure adds significant time to the procedure.
The present invention is directed at solving at least some of the afore-mentioned problems.